1. Field of the Invention
The present invention relates to an etchant and more particularly, to an etching treatment agent used for fine treatment of insulating film such as silicon oxide or the like at a high speed and uniformity in the manufacturing process of semiconductor devices.
2. Description of the Related Art
Cleaning, etching, and patterning of a wafer surface and a finely-manufactured surface with higher cleanliness, higher precision, and more advanced performance are becoming more important with the tendency for increasingly higher integration and higher capability of integrated circuits in the wet process of the manufacturing process for semiconductor integrated circuits.
Both a solution of hydrogen fluoride (HF) and a mixed solution (buffered hydrogen fluoride) of HF and ammonium fluoride (NH4F) are applied for the purpose of cleaning and patterning as a surface treatment agent for fine surface treatment, but in order to acquire submicron ultra high integration, higher performance and higher capability is increasingly required. Further, although the wafer currently averages 8 inches in diameter, it is predicted that the wafer will be 12 inches in diameter by the year 2000.
A wet etching method for a wafer in the conventional case is the batch method of putting 25 to 50 sheets of wafer into a cassette, soaking the whole cassette into an etching bath, and subjecting the cassette to etching treatment. Further, a cassette-less type of cleansing method is employed for preventing drag-in of a solution.
The batch method described above has the advantage of high throughput because of enabling concurrent etching onto a large number of wafers, but has the disadvantage of low uniformity of etching within each surface of the wafers. This low uniformity is more noticeable when the wafer size is larger, such as the 12 inch diameters predicted in the future, and it is conceivably difficult to obtain etching uniformity within the surface of a wafer in current batch processing. In addition, the difficulty will be more serious in accordance with increased tolerance necessary in the art.
And for this reason, in order to enhance etching uniformity, a single wafer processing type etching method in which an etching solution is supplied onto a wafer being rotated has been considered. This method has the advantage of enhancement of the uniformity, but has a disadvantage in that a long time is required for the some throughput as batch processing.
Namely, the buffered hydrogen fluoride solution (BHF) having conventionally been applied is prepared for application usually by mixing 40 percent NH4F and 50 percent HF in various mixing ratios (such as in a range of 400:1 to 6:1), and etching speeds to silicon oxide film by this BHF are in a range from 27 nm/min to 115 nm/min.
The time required for etching onto 50 sheets of wafer each with oxide film having a thickness of 500 nm in the batch method, with BHF obtained by mixing HF and NH4F in a ratio, for example, 7:1 is about 5 minutes. But, if the treatment is carried out by the cut sheet type of method with this BHF, the treatment for only one sheet thereof requires about 5 minutes, and so it is understood that the treatment for 50 sheets thereof requires the time 50 times as much as that by the batch method, namely 250 minutes.
Such an enormous time is unrealistic for a line of mass production facilities, and in order to introduce a single wafer processing type etching method into the line of mass production facilities, the treatment time for one sheet has to be reduced. The level of the treatment capability required for the cut sheet type thereof may be decided through the designing of the entire semiconductor manufacturing process, but it is required, at least in order to make throughput maximum, to make wafer passing between devices for treatment smoother so that a retention time is made minimum. For that purpose, at least the same level of treatment capability as that of a dry etching device is required.
The current single wafer processing dry etching process has the capability of etching onto silicon oxide film having a thickness of 500 nm to 1000 nm at around 25 to 30 sheets/hour. Accordingly, an etching solution having the capability of treatment at etching speeds in excess of 200 nm/min is required.
However, the conventional type of etching solution, of which etching speeds are required, dissolves and separates the resist at the same time, and for this reason it is difficult to execute high-speed treatment for a fine pattern on the insulating film.
Conventionally there exists no such etching solution where etching treatment can be effected onto a fine pattern with high speed.
An object of the present invention is to provide, under the situation described above, an etching treatment agent which can etch an insulating film with high speed without damaging the resist pattern.
Another object of the present invention is to provide an etching solution enabling treatment with realistic throughput when the insulating film etching process in the semiconductor manufacturing process is replaced with the single wafer processing etching treatment method.
Further, another object of the present invention is to provide an etching treatment liquid for preventing roughness on the surface of a semiconductor after etching.
According to the present invention an etchant is applied for the purpose of etching treatment onto insulating film with a resist as a mask formed on a substrate, containing 8 percent by weight through 19 percent by weight of hydrofluoric acid, 12 percent by weight through 42 percent by weight of ammonium fluoride, and a hydrogen ion concentration of 10xe2x88x926.0 through 10xe2x88x921.8 mol/L. Preferably, the concentration of the hydrofluoric acid is set at 15 percent by weight through 19 percent by weight. An etchant according to the present invention is applied for the purpose of etching onto silicon oxide film with a resist mask formed on a substrate with etching speeds to the silicon oxide film of 200 nm/min or more and a film-reduction rate of the resist of 50 nm/min or less.
Preferably added to the etchant according to the present invention is 0.001 percent by weight through 1 percent by weight of a surfactant.